Signaling system



Nov. 28, 1939..

H. w. DUDLEY SIGNALNG SYSTEM Filed Aug. 25, 1937 2 Sheets-Sheet 1 mfVEA/TOR H. W DUDL EV Nov. 28, 1939. H. w. DUDLEY SIGNALING SYSTEM FiledAug. 25, 1937 2 Sheets-Sheet 2 A 7` .TORNE Y Patented Nov. 28, 1939UNITED sTATEs PATENT oFFicE I mames l lHorner W. Dudley.

to Bell Telephone New York, N.' Y.,

Garden City, N. Y., asslxlor Laboratories, Incorporated, a corporationof New York Application August z5, 1931, serial No. 160,759

11` (ciglia-100.1)

This invention relates to signaling systems and has for its main objectto provide apparatus for making a visual record of a complex speechfrequency message in a form capable of being readily interpreted by theeye.

In the two most common forms of speech communication the spoken wordwhen Areceived byl the ear gives complete information, While the other,the written word, gives only partial information to the eye. Thispartial information conveyed tothe eye by the written word insures thetransmission of intelligence as far as the word content goes, but itomits all "those thingsthat enter into the voice, such as stress,intonation, duration, brogues and accents, slurring and weakening ofsounds and the various other characteristics which go to make -upspeech. The limitations of the written word are obvious when oneconsiders that the production of speech sounds corresponds to varyingsix or more elements ofthe vocal system, such as-the lung pressure, thevocal cord tension, the position of the lips, teeth, front and reartongue and uvula, while the written Word corresponds to using a singlevariable to transmit the information.

In its preferred embodiment, this invention provides means for producinga visual record which gives more complete information about the of thevocal system that are involved in production); and the rate at whichthese vary.

Speech signals satisfy the condition for possible frequency*l rangereduction iii outstanding manner for inone stage of speech production,namely, the muscular, there is a very simple set of controlled motionsof the muscular parts making up the speech signal. Several muscularelements move to form a speech signal, but their rates of motion are theslow muscular or syllabic frequency rates. As an example, the lips movefor ordinary-speech at a cyclic rate not ordinarily exceeding 7 cyclesper second for the fundamental or basic motion. Several other parts oftbc vocal system, such as the lungs, uvula, tongue, and teeth move also,but they too move at slow rates not ordinarily exceeding even these twotypes have a basic rate of change nature of the message than isobtainable from the written word; more particularly `to provide for theeye in a form capable of readyinterpretation a record igivingapproximately vas complete information as to the character of themessage as theear receives from the spoken word. Preferably, inaccordance with this invention, the complex Yspeech signal is notrecorded directly,

.but is rst reduced to a low frequency range ,Qfrom 0 to 20 cycles, forexample) without losing f vany of the defining characteristics of thespeech With this frequencyV reduction of the message to a low frequencyrange the visual record may be more readily read or interpreted by theviewer than would be possible if the record 'covered the entire speechfrequency range. The

J invention may, therefore, be regarded as an improved type oftelegraphized speech.

The information transmitted by speech does no1; absolutely require allof the frequency'space l allotted to it by the human voice. A specificcase `can be worked out as to how wide a frequency band is required as aminimum, forv example, by determining and taking account `of the numberof independent variables or parameters involved in speech production,(that is, the number of the independently movable physical elements at ahigher fundamental frequency is that of the `vocal cords where thefundamental frequency for men is around 125 cycles per second and forwomen over 200 cycles per second. This mo tion differs from the othersmentioned in that it is a natural frequency of stretched cords. Thetension ofthe cords is controlled voluntarily and can be changed only atslow muscular or syllabic rates. The vocal cordsnot only have a highfundamental frequency but they also give a wave shape which'is rich inharmonics up to several thousand cycles per second. The `vocal cordshave asteady energy source in the lung pressure which produces airvibration at. their natural frevof not over 'I cycles per second. Thefirst motion closing with air forced through to form a hissing sound mayoccur between the lower lip and upper teeth as for the f sound orbetween the tongue and front part of thehard palate as for the "s sound,or at other places for other unvoiced or breathed sounds; Such soundshave a continuous frequency spectrum with no definite fundamentalfrequency. It will bev noted that in all such unvoiced sounds thevolitional control is again applied at the low frequency muscular orspeech range.

syllabic rate, generally not exceeding 7 cycles per second.

From the foregoing detailed discussion of they mechanics of speech soundproduction, it is seen that the various speech sounds are produced byvoluntarily controlled variations in the muscular systems at slowsyllabic frequency rates of 7 cycles perscond or less. The importantmuscular elements or variables used ln speech production are eight innumber as follows: lung pressure; vocal cord tension and position; rearmouth resonance chamber; front mouth resonance chamber; opening fromfront to rear resonance chamber; mouth opening; position of uvula;position of any stricture in the sound path.

Since the important muscular variables are only eight in number, it isseen that the total frequency range required to produce sounds for thevocal systems is very limited, it being limited in Afact to the numberof such'variables multiplied by the frequency range required to expressthe motion of each, which may be about 14 cycles per second if thereasonable assumption is made that the fundamental rate of change plusits first upper harmonic defines the-motion reasonably well.

A simple ideal system for frequency range reduction in speech vwouldbeto analyze the speech sound to determine what'the important motionsare and then prescribe a narrow frequency band, say, of 20 cycles inwidth to dene each motion, but it is difficult, if not impossible, to doit in this simple way because of the analyzing diiiiculties. Thus, forexample, it is very dimcult to determine from a speech sound just whatposition the tip of the tongue had in its production.V

However, it is reasonably simple to do this by the use ofequivalentparameters. So long as the parameters are entirely independent we knowmathematically that we can use any parameters we choose. Not only canthey be chosen in any fashion'provided they are independent, but if theyare not entirely independent, more parameters can be chosen to make upfor the lack of independence. Thus, as an example, the sounds can beanalyzed into independent variables that are easily determined such asthe power in each of several small: frequency subbands within the Thepower in each subband is not entirely independent `of that in theothers, but is sufficiently so that the average power level in say eightor. ten subbands of the speech range will give us a very satisfactoryset of parameters for speech definition. 'I'his analysis ofthe powerlevel in small frequency subbands is preferably done electrically bycircuit arrangements described hereinafter. '4 A In one specific aspectof this invention the speech message is analyzed electrically for itsfundamental frequency andthe average power in properly chosen subbandsof frequency. In analyzing for the fundamental frequency aunidirectional current is produced whose magnitude defines the frequencyof the fundamental frequency and whose magnitude varies with the sy1-'labic rate of change in the fundamental frequency. The magnitude of theunidirectional current will also be indicative of the presence of anyunvoiced sounds which, having no definite fundamental frequency, willresult in la substantially zero value of the defining unidirectionalcurrent. An analyzer may -also be arranged to produce separateunidirectional currents each defining the average power level in achosen subband of the frequency range of the message.

'I'hese defining unidirectional currentsin accordimpressed upon separaterecording devices having needles arranged to make a written record on amoving strip of paper either in the form. of a. scratch on the surfaceorin the form of an inked or pencilled line. The plurality of separaterecv ords so formed may be'viewed collectively and readily interpretedafter a little training. Providing there is a defining current for theaverage power level in, say, eight to ten subbands of the speechfrequency range the visual record produced in the above manner will giveto the viewer substantially Vas complete information as if the -viewerhadheard directly the spoken word. This composite record will also bemuch more readily interpreted and understood than if one attempted,without frequency range reduction, to make directly a single record ofthe complex speech 4wave for the entire frequency rangeof speech. Thepresent invention is therefore particularly adapted for conveyinginformation to the deaf since the information is far more complete thancould be obtained by lip reading or by the written word. Other uses,however, are contemplated such as a substitute for` the existing type oftelegraphy where the telegraph record comprises merelya single variableusually a series of dots and dashes according to a particular code.

Referring to the drawings:

Fig. 1 is a schematic circuit embodying one form of this invention formaking an accurate visual record of a speech message;

Fig. 1A is a fragmentary view of a type of recording device which may beused in the system of Fig. 1; f

Fig. 2 is lillustrative of the type of record obtained forlcertainspoken words by the use of the apparatus of Fig. 1;

' Fig. 3 is a simplified form of the invention; and

Fig. 4 is a representative record obtained by the system of Fig. 3.

Speech may be regarded as having a dual characteristic; On the one handwe have fixed parts or elements setting up oscillatory waves containinghigh frequency patterns. On the other hand we have varying parts orelements setting up modulatory'waves of low' syllabic frequency patltern. The fixed features include (a) the existence of definite frequencysubbands in which the power distribution is uniform at `any giveninstant; (b) the existence of a frequency spectrum that alternates froma continuous type of spectrum with no definite fundamental frequency toa discrete type with varying fundamental and with al1 the upperharmonics always present;

and (c) the .fact that time variations of the fundamental frequency andof the power in the frequency subbands occur only at syllabic frequencyrates. The variable features include (a) the magnitude of the averagepower at each subband and (b) the nature of the signal spectrum bandinto which the speech signal is divided."

speech frequency band into about eight or ten.

subbands and provide means for indicating the syllabic rate of change ofthe average power in each subband. In Fig. 1 the speech signal isdivided into ten subbands. The subbands may be of unequal width, sinceeach subband may have a width depending upon its importance function inthe production of speech as described, for exai'nple, in my UnitedStates Patent 2,151,091, issued March 21, 1939 on Signal transmission..

'I'he second-mentioned variable feature of speech concerning whichinformation should be transmitted is the nature of-the speech spectrumas to whether it is a continuous spectrum without any denite fundamentalfrequency or whether it is a discrete spectrum and in the latter case asto what is the frequency of the fundamental frequency for each voicedsound analyzed. This information is transmitted and recorded in a simplemanner by the apparatus of Fig. 1.

In the arrangement of Fig. 1 the speech or other vocal sound to beanalyzed is picked up by a suitable high quality microphone 20 andamplied to a desired level by an amplifier 2| whose output is dividedinto a frequency pattern measuring circuit FP and an amplitude patternmeasuring circuit AP. The frequency pattern measuring circuit FP takesadvantage of the fact that l in vowels and in other sounds vhaving avdecided fundamental frequency in the range from 80 to 320 cycles, thereis a high-power level, while in sounds like the sibilant consonantswhere the power is in the continuous spectrum rather than 'a dicretespectrum, the power level is much lower.

When a high level discrete spectrum is received from amplifier 2l thefrequency pattern measuring circuit FP sends to the yrecordingmilliammeter 22 a current of a magnitude indicating what the fundamentalfrequency is, but not indicating anything about the amplitude of thecurrent of the fundamental frequency. When a. lowv level continuousspectrum speech signal is received from amplifier 2| the output currentfrom channel FP is substantially zero and hence no current is applied tothe recording-device 22.

Referring more particularly to the details of the circuit FP a band-passfilter Fo selects the band from 50 to 400 cycles of the voiced signal soas to be surel to include the fundamental frequency, if any.; The outputof this band-pass filter Fc is sent through an attenuation network E1 ofa type oftenjtermed an equalizer which has a loss increasifng withfrequency for the purpose of insuring that the fundamental frequencycomes out at a higher level than any of its upper harmonics that may bepresent. For practical purposes this puriiies the fundamental tone. Nextthe output from this equalizer Ei is fed to a constant output amp Nr LAso that from this amplifier there is obtain ,i essentially a singlefrequency, the fundaxsitiental Ifrequency .of the speech signal at aconant p werlevel regardless of what thel frequency This fundamentalfrequency may be from about 50 cycles to 400 cycles. Next we pass thispower y throughian equalizer En. which has a characteristie reverse -tothat of .network E1 in that the output l.ffrom equalizer-Ez increases asthe frequency/ increases. This output is sent through a copper-oxidedetector Do which gives essentially a direct current bias whichiluctuates as the fundamental frequency of speech fluctuates, that is,at a syllabic frequency. The detector output is then sent through alow-pass filter Fao cutting oif at 20 cycles so that the unwanted higherfrequency products are eliminated. This output is now used as a biasingcurrent applied to the winding of the recording milliammeter 22 wherebyits recording needle 23 is moved from vits zero position an amountproportional to the defining current from filter Fao. 'I'hat is, thedeparture from its normal axis of the trace made by needle 23 on themoving paper strip 24 will be proportional to the frequency ofthe-fundamental frequency so that the fundamental `frequency will beaccurately indicated on the record sheet for each speech component. Fora voice with aohigh pitch the trace made by needle 23 will depart widelyfrom its zero axis, while for a voice with a low pitch the trace will becloser its zero axis and the position of the trace will vary with anysyllabic variations in the pitch of the voice.

However, when the frequency pattern circuit FP receives a speech signalhaving a continuous spectrum such as whena sibilant consonant sound lisimpressed on the microphone 20 the entire frequency spectrum is at a lowlevel with no frequency emphasizedover the others. Hence, for such soundthere will be substantially no' energy output from low-pass filter F3nand hence milliammeter needle 23 will remain substantially on its zeroaxis.

There remains to be described the apparatus for analyzing the speakersenergy in the different frequency subbands of the speech frequency rangein order to determine the amplitude pattern characteristic of eachspeech signal.- The amplitude pattern measuring circuit AP of Fig. 1 isessentially a circuit for measuring how much power there is in thespeech signal in chosen small frequency bands and for transmitting thisinformation by proportional currents to a plurality of .recordingdevices, one for each subband. The amplitude pattern circuit AP at theoutput of amplifier 2l is divided by suitable band-pass filters-F1 toF1o into ten frequency subbands. As shown on the drawings, channel AP:receives the vspeech frequencies in the band from zero to 250 cycles;channel AP-z receives the speech frequencies in the band from 250 to 550cycles; channel AP: receives the speech frequencies in the band from 550to 850 cycles; channel AP4 receives thespeech frequencies in the bandfrom 850 to 1150 cycles; channel AP receives the speech frequencies inthe band from-1150 to 1450 cycles; channel APs receives the speechfrequencies in the band from 1450 to 1750 cycles; channel AP'z receivesthe speech frequencies in the band'from 1750 to 2050 cycles; channel APsreceives the speech frequencies in the band-from 2050 to 2350 cycles;channel APg receives the speech frequencies in ythe band from `2350 to2650 cycles; and channel APm receives the speech frequencies in the bandfrom 2650 to 2950 cycles. These bands have been chosen for the purposeof illustration. Obviously, other bands may be found preferable forparticular circuits and may be so used without departing from theprinciples involved. s

Considering the channel APi, for example, the output from the zero to250 cycles band-passv filter F1 is fed to detector D1 which may be, for

are passed-through a 20 cycle low-pass filter Fn fest subband. zero to250 cycles,

and used to energize a recording milliammeter 4| so that the amplitudeof the vibrations of needle 5| of device 4| deiines the average amountof pwer of each speech component in the frequency band from zero to 250cycles and the amplitude of the needle vibrations will increase ordiminish at a syllable rate in response to the syllable vari- :ions ofthe po'wer level in the designated sub- Channels AP: to APm are similarto channel AP; just described except for the frequency range analyzed byeach channel. The defining currents from channel APz are recorded byneedle 52 of milliammeter 42; the defining currentsl from channel AP:are recorded by needle 53 of milliammeter 42; the deiining currents fromchannel AP; are recorded by needle 54 of milliammeter 44; the deningcurrents from channel APs are recorded by needle 55 of milliammeter 45;the defining currents from channel APs are recorded by needle 56 ofmilliammeter 45; the dening currents from channel AP: are recorded byneedle 51 of milliammeter 41; the defining currents from channel AP. arerecorded by needle 58 of milliammeter 48:-the defining currents fromchannel APa'are recorded by needle 6 9 of milliammeter 49; and thedeilning currents from channel APm are recorded by needle 60 ofmilliammeter 50. Filters F1 to F1o are alike except as -to the frequencyband passed, as indicated on the drawings. Detectors Du to Din may beall alike and lters Fao to F40 are all alike in that they suppress allfrequencies above 'cycles.

'I'he apparatus of Fig. .1, therefore, utilizes one milliammeter 22 torecord the frequency variations of the fundamental frequency of thespeech message and utilizes ten milliammeters 4| to 54 to record theaverage power level in the ten subbands of frequency into which thespeech frequency band is divided by the band-pass lters F1 to F1o. Theeleven milliammeters are prefer- Y ably so constructed and mounted thattheir'traces on the moving strip 24 are arranged compactly but withoutany overlapping. The paper strip 24 may be moved at a constant speedpast the line of recording needles by any suitable mechanism such as anelectricmotor, 55 geared to a l cylinder I4 around which the paper isrolled after the record is made.

'I'he character of the deilning patterns set up by the elevenmilliammeters is shown in Fig. 2 for two typical words "sharp" and"void. The lowest-trace 41 is that of the pitch or fimdamental frequencyof the tone as recorded by milliammeter 22. The next trace 44 gives ameasureof the average energylevel in the lowas recorded by milliammeter4|. upwardly onA the paper strip 24 the succeeding traces are forprogressively higher subbands as indicated at the left of the iigure,trace 0I, for example, giving a m e of the average energy level in thehighest subband, l2650 to 2950 cycles. Since the pitch record 41 for thedistance from zero to .2 second measured along an arbitrary time scalelies substanuauy along the zero axis il for the milliammeter 22 it willbe obvious that the recorded sound during this time interval is anunvoieed sound without any deilnite fundamen-l tal. For the same timeinterval the-ten traces above the pitch trace show substantially xeropower level vfor the lower bands but withV deilnite Y power levels intheir upper bands particularly in the 2350 to 2650 cycle band and the2650 to 2950 cycle band indicating deilnitely an unvoiced aisance sound.The collective picture made by the traces for the ten subbands is thatgiven by only one sound, namely, the sound sh. As the a sound isrecorded beginning about the vertical line 1|, 'thepitch record 11indicates a voiced sound with a definite fundamental of a frequencyproportional to the distance between the trace 61 and its zero axis 10while the energy level of .the sound is prominent in the lower subbandsas well as in .the upper subbands. The composite traces just to theright oi' line 1| give an accurate picture of the power leveldistribution for the sound "a as in sharp and will be readilyinterpreted as representing that sound by one trained in observing suchrecords. The record of the remainder of the spoken word sharp" is shownstill farther to the right in Fig. 2.

Another portion of the strip 24 in Fig. 2 snows the deilning traces forthe spoken word void as recorded by the eleven milliammeters of theapparatus of Fig. 1, Distinctive differences will be noted between thetracesfor the word sharp and the traces for the word "void.

The milliammeters employed as Velements 22 and 4| to 50 of Fig. 1 maybe, for example, of the type disclosed in Fig. 1A which is of the movingcoil type. 'I'he magnet structure 13 has opposed pole-piecessubstantially surrounding a smalla coil 14 mounted for rotation in anysuitable manner, not shown, in response to currents applied to` the coilfrom any one of the eleven channels of Fig. 1. 'I'he frame whichsupports coil 14 has a lightweight extension or wire 15 which, at itsouter end, supports a holder for a recording needle 16. As previouslystated, needle 16 may be arranged either to make a written record in theform of a scratch on the surface or in the form of an inked or penclledline.

It will be apparent from the above that the .apparatus of Fig. 1produces a type of visual symbolic speech involving the principle ofanaof speechV sounds. It is to be emphasized 'that the system oftelegraphized speech proposed by this invention is inherently phoneticin nature. In recording the speech sounds from a talker with the systemot Fig. 1 itis only the phonetic sounds which h e produces that arerecorded and not the artiilcial printed symbols that-'are ordinarilyemployed. 'Ihe printed word and the ordinary telegraph code useartincial speech symbols and the mind is ordinarily trained to learn adiiferent speech language for the eye from that for the ear. When onelistens to speech it isl of course phonetic speech that he hears. Alsothe eye in lip reading is using a crude form of phonetic .terms ofspeech symbols rather than in terms.'

speech. -In that respect, the telegraphized speech of this inventioncorresponds to lip reading rather than the earlier forms of `visualsymbolic speech. It should be noted that symbolic phonetic speech asgiven by this invention is an advantage and not a handicap because ittells the story of the speech as spoken, including the emotional contentas well as the intelligence content. a

Fig. 3 shows a speech recording circuit somewhat like that of Fig. 1 butgreatly simnliiied.

The simplification results from the use of only three of the elevenchannels of Fig. 1 and as a result the speech denning signals of Fig. 3may be readily transmitted over a telegraph line by amplified byamplifier 84 the output of which leads to a frequency pattern measuringcircuit FP and an amplitude pattern measuring circuit AP. The frequencypattern channel FP of Fig. 3 is employed to differentiate between avoice and an unvoiced sound, while the two channels of the amplitudepattern circuit 81 and 88 are employed to define the average power levelin two selected subbands of the speech frequency range. 'Ihe frequencypattern circuit Fl? is identical with the circuit FP of Fig. 1 andcomprises in tandem a band-passlter 15 passing the band between 50 and400 cycles; an equalizer 11, a constant ontput amplifier 18, anequalizer 19, a detector and a low-pass filter 8| passing the bandbetween zero and 20 cycles. As explained in connection with the channelFP of Fig. 1 there will be a substantial output current from lter 0| fora voiced sound but a substantially zero output for an unvoiced sound.

In the amplitude pattern circuit AP of Fig. 3 only two channels areemployed, one channel 81 containing a band-pass' filter 86 passing aband between 400 and 800 cycles of the speech fre# quency message fromamplifier 04 `while the other channel 88 comprises a band-pass filter 89passing the band between 2300 and 2900 cycles.' These two channels havedetectors 90 and 9| similar to detector 80 and also have lowfpassAfilters 92, 93 similar to low-pass lter 8| in that they pass only theband between zero and 20 cycles.

The unidirectional current constituting the output of filter 92 whichdefines the average i power level lin the speech frequency subband from400 to 800 cycles for each component of the speech message is impresseddirectly upon a line 94, such as a telegraph line, and thereforeconstitutes the main telegraph signal sent over the line. The higherband channel output from filter 93 is used to control the amount of acarrier frequency such as 69 cycles which is transmittedover the line.Oscillator 95 may be a source of 60 cycle current which is connected toa suitable modulator 96 through a filter. 91 which passes only 60 cyclecurrent. The zero-to 20 cycle current from filter 93 which deiines thespeech characteristics in the 2 300 to 2900 cycle band is also impressedupon modulator 96 whereby the 60v cycle carrier is modulated by the zeroto 20v cycle band from channel 88. The output from modulator 96 passesthrough a 40 to 80 cycle band-pass filter 98 so that both sidebands aswell as the carrier are impressed on line 949.10m; with thelow-frequency 4signal from channel-81.

-At the remote station a recording milliammeter 99 is connected directlyto line 94 and milliammeter 99 is preferably of a type that respondsefllciently to a' frequency of 80 cycles ciu-higher.

'It follows that indicating needle |00 will vibrate at th'e 60 cyclerate with the height of its vibrations varying with the control currentfrom channel 88 while at each instant the middle point of each swingwill vary from the normal axis for the needle an amount controlled bythelow-frequency current from channel 81. As in Fig. 1 the indicatingneedle |00 is adapted to form a trace on a moving strip of paper |05,the character of the trace being illustrated more clearlyin Fig. 4. Line94 also has a biasing battery |0| which is impressed on the recordingmilliammeter 99 with a polarity determined by the presence or 5 absenceof the fundamental frequency measuring current from the'pitch channel FPand therefore with one polarity for a voiced sound and with the oppositepolarity for an unvoiced sound. This diiferentiation is accomplished byhaving the out- 10 put from filter 8| connected to a relay |02 whosecontacts in an obvious manner constitute a reversing switch fo'r battery|0|. With anunvoiced sound there is substantially zero output fromfilter 0| and hence relay |02 will remain un- 15 operated and positivebattery is connected to the upper wire of line 94. vThis will produce adirect current which biases milliammeter 99, for example, so that for anunvoiced sound the needle |00 in the absence of any control current from2 channels 81 and 68 wouid trace a straight line |06 of Fig. 4 whichline will be termed the unvoiced axis. However, if the speech sound toberecorded is a voiced sound tnere will be a substantial output currentfrom filter 8| to operate relay 25 |02 and change the batteryconncctionsso that now positive battery is connected to lower wire ofline 94. This will cause needle |00 in the absence of any controlcurrent from channels 81 and 88 to trace a straight line |01 which willbe termed 3 the voiced axis.

The traced record of Fig. 4 is for the words sharp and void as in Fig.2. The i'lrst portion of the traces for the sound sh is along axis |06showing that it is an unvoiced sound and the fact that the trace is onboth sides of axis |06 shows very little energy content in the 400 to800 cycle band as compared with the energy content in the 2300 to 2900cycle band. The voiced sound ar causes relay |02 to reverse the batteryconnec. 40

tions and cause the trace to lie adjacent the voiced axis |01 and itwill be noted on the arbitrary time scale shown on Fig. 4 from about .23second to .5 second the median line for the 60 cycle trace lies entirelyon one side of the axis 45 |01 at a distance controlled by the energydefin ing currents from channel 81. The character of the trace for thespoken word void will be obvious from the above description, forexample, for the sound v the record for a short interval 50 is along theunvoiced axis and then jumps to the voiced axis but in each instance thehigh frequency vibrations of the trace are of very low amplitudeindicating small energy output from both channels 81 and 88.

Ihe composite trace produced'by the indicating needle |00 isoi' asuiliciently defining nature to enable one, after a little training. tointerpret accurately the speech message recorded thereby.

The system of Fig. 3 may be termed a form of 60 direct speech telegraphysince. at the sending end, the sounds of a talker are directly convertedinto vdefining currents which pass over line 94 where while stillobtaining a satisfactory and accurate record ofthe speech. It will beapparent that if desired the three channels of the analyzing system ofFig. 3 may have their defining currents I5 impressed separately ondifferent milliammeters in the same manner as in the system of Fig. 1.

It is also to be understood that the defining currents from the elevenchannels of theI system of Fig. 1 may, if desired, 4be transmitted overa line or other communication channel to a distant receiving stationwhere the recording milliammeters 22 and 4| to 50 are located, althoughmore complicated apparatus will obviously be required to enable theeleven control currents to be transmitted simultaneously.

Since the frequency pattern circuit FP of Fig. 1 and Fig. 3 tends tohave more inherent delay than the associated amplitude pattern branchesit will generally be advisable to introduce a certain amount of delay incommon to all the amplitude pattern circuits to compensate forv thisdifference. Thusin Fig. l an electric delay equalizer DE is connected inchannel AP so as to be common to all channels AP; to APm, while in Fig.3 a delay equalizer |09 is common to channels 81 and 88.

The above circuits for forming telegraphized speech symbols which canreadily be read by the eye to give an automatic speech telegraph circuitare merely representative of the'invention since it will be evident tothose skilled in the art that many modifications may be made withoutdeparting from the spirit of the invention as defined in the appendedclaims. For example, if desired, the recording milliammeters employedmay be of the logarithmic type rather than the linear type.

What is claimed is:

1. A recording system for a message 'represented by a complex`electrical wave of a wide band of audible frequencies. said systemcomprising means for selecting a number of substantially independentcharacteristics'of said wave,rmeans for producing a plurality of lowfrequency currents each having a fundamental frequency of less than tencycles per second and each defining one of the characteristics of saidwave, and means' controlled by said low frequency currents for producinga visual record from which the word content of said message may beinterpreted by the eye. q

2. A recording system for a message represented by a wide band ofaudible frequencies, said system comprising means'for dividing saidmessage into a plurality of'frequency subbands each of a limitedfrequency range, separate means for deriving from each subband a lowfrequency wave of a fundamental frequency of less than ten cycles persecond, which wave denes the average energy level in the subband, andmeans for producing a separate visual record of each of said definingwaves for enabling the eye to interpret the word content of said messageby the inspection of said records. v

3. A recording system ,for a speech message represented by a complexelectrical wave of a wide band of. audible frequencies, said systemcomprising means for dividing said wave into a plurality of frequencysubbands, separate means for demodulating each subband, and meanscontrolled by the demodulated currents for producing a visual recordfrom which the word content of said message may be interpreted by theeye.

4. A recording system for a message represented by a complex electricalwave of a wide band of audible frequencies, said system comprising meansfor selecting a number of substantially independent 'characteristics ofsaid wave, means for producing a plurality of low frequency currentseach having a fundamental frequency of less than ten cycles per second,and each defining one of the characteristics of said wave. analyzingmeans for producing from said waves. low frequency wave of a fundamentalfrequency of less than ten cycles per second whose amplitude definesvariations in the frequency of the fundamental frequency of said complexwave, and

' means for producing a visual record of said low frequency currents andsaid low frequency wave for enabling the eye to interpret the wordcontent of said message bythe inspection of said record.

5. A recording system for a message represented by a complex electricalwave of a wide band of audible frequencies, said system comprising meansfor dividing said wave into a plurality of frequency subbands; separatemeans for demodulating each subband, analyzing means for producing fromsaid wave a low frequency wave of a fundamental frequency of less thanten cycles per second whose amplitude defines variations in thefrequency of the fundamental frequency of said complex wave, and meansfor producing a visual record of said demodulated currents and said lowfrequency wave for enabling the eye to interpret the word content ofsaid message by the inspection of said record.

6. A speech recording system comprising means for converting speech intoa complex electrical wave containing a wide band of frequencies ofimportance in speech, means for dividing said wave into a plurality offrequency subbands, separate means for transforming each of saidsubbands into a narrow band of frequencies whose upper frequencylimit'lies well below the average fundamental frequency of speech withthe amplitude of each narrow frequency band defining the average energylevel in the subbandfrom which it is derived, and means controlled bythe amplitude variations of said narrow frequency bands for producing avisual record from which the word content of the recorded speech may beinterpreted by the eye. 1

7. A speech recording system comprising means for converting speech intoa complex electrical wave containing a wide band of frequencies ofimportance in speech, means for dividing said wave into a plurality offrequency subbands. separate means for transforming each of saidsubbands into a narrow band of frequencieswhose upper frequency limitlies well below the average fundamental frequency of speech with theamplitude of each narrow frequency band denning the average energy levelin the subband from which it is derived, means for producing a Vvisualrecord of the amplitude variations of said narrow frequency bands, andmeans for producing as a part of said visual recor'd an indicationdistinguishing voiced portions of said wave from unvoiced portions ofsaid wave, said indication for voiced portions of said complex wavebeing wholly independent of the amplitude of the fundamental frequency..y

8. A recording system for a message represented by a complex electricalwave of a wide band of audible frequencies, said system comprising meansfor deriving said wave into a plurality of frequency subbands, aseparate rectifier for each of said subbands, an output circuit for eachrectifier, a separate filter in each output circuit for suppressingfrequencies in excess f about twenty cycles per second, and means conltrolled by the filtered currents from each rectifier for producing avisual record from which the mismos word content of said message may beinterpreted by the eye.

9. A transmission system comprising means for converting speech into acomplex electrical wave containing the frequencies of importance inspeech, filter means for dividing 'said wave into a plurality offrequency subbands each of a limited frequency range a rectifier foreach of said subbands, a recording instrument simultaneously responsiveto the output of said rectifiers A and additional means for controllingsaid instrument to distinguish between voiced portions and unvoicedportions of said wave.

10. In a transmission system, means for converting speech into a complexelectrical wave containing frequencies of importance in speech, filtermeans for dividing said wave into a plurality of frequency subbands eachof a limited frequency range, a rectier for each of said subbands, alimited frequency line connected to the output of vone ofsaid rectiers,a source of carrier frequency, means for impressing on said line saidcarrier frequency modulated by the low frequency output of another ofsaid rectiers, a source of direct currentfmeans for vconnecting saiddirect current source'to said line with one polarity for the voicedportions of said wave and the opposite polarity for the unvoicedportions of said wave, and a receiving station connected to said linecomprising a recording device for producing a visual record of thecombined currents received from said line.

11. In a transmission system, a telephone transmitter for convertingspeech into a complex electrical wave, a line connected to saidtransmitter, a plurality of channels connected to said line, eachchannel comprising a lter for passing to its respective channel only alimited band of speech frequencies, each lter passing a differentfrequency band, a rectier in each channel, a

movable message tape, a plurality of recording devices forsimultaneously making separate visual .records on said tape on adjacentportions of said tape, each of a plurality of said devices beingresponsive to the output of one of said rectiers, means for producing alow frequency current the amplitude of which defines thevfrequency ofthe fundamental frequency of the voiced portions of the converted speechsignal while lproducing a substantially zero current for the unvoicedportions of the speech signal, a separate one of said receiving devicesbeing responsive to the dening current of said last-mentioned means.

HOMER. W. DUDLEY.

